The present invention relates generally to video and graphics display devices, and more particularly to the illumination of display devices.
Display devices are commonly used in televisions or computer monitors for displaying color pictures or information. One type of display is xe2x80x9cself-luminantxe2x80x9d, i.e., one which generates light required for its operation, such as a cathode ray tube (CRT). For example, televisions and CRT computer monitors are self-luminant because there are phosphors on the screens which actually glow and emit light. Another type of display is xe2x80x9cnon-self-luminantxe2x80x9d, i.e., one which requires an external source to supply the light required for its operation. For example, slide projectors are non-self-luminant because they have projection lamps that shine light through the display image (the slide) and onto a screen which simply reflects the light. Non-self-luminant displays are classified into reflective and transmissive types. In a reflective display, external light is reflected off a surface of the display to produce an image. In a transmissive display, the external light is allowed to pass through the display to produce the image.
Recently, display devices based on electro-optical materials such as ferro-electric liquid crystals have been introduced. Such display devices can form part of a miniature, wearable display, sometimes called an eyeglass display or a microdisplay, and also can form part of a front- or rear-projection display. The liquid crystal material, which forms the optical component of the display device, is placed directly on top of a silicon integrated circuit, which is divided into a two-dimensional array of picture elements (pixels) that define the pixels of the display device. The signals used to turn the individual pixels of the display device on and off are generated on the silicon integrated circuit.
The display device typically includes a reflective light valve, an illuminant source which generates light that illuminates the light valve, and output optics that focus the light to form an image. The light valve is composed of a reflective spatial light modulator, a polarizer, a beam splitter and an analyzer. In operation, light generated by the illuminant source passes through the polarizer. The polarizer polarizes the light output from the illuminant source. The beam splitter reflects a fraction of the polarized light output from the polarizer towards the spatial light modulator. The spatial light modulator is divided into a two-dimensional array of picture elements (pixels) that define the pixels of the display device. The spatial light modulator will reflect the light in a manner such that the plane of polarization of the light will or will not be rotated. The beam splitter transmits a fraction of the light reflected by the spatial light modulator to the analyzer. Light is output to the output optics from the light valve which causes the pixels to appear bright or dark depending on whether or not its direction of (polarization was rotated by the spatial light modulator.)
In all the above systems, there are three conventional methods of rendering color images in a display device. The three methods render a color image using the conventional red-green-blue (RGB) system. The first method involves using three separate pixels that are spatially located near each other. Each of the pixels represents one of the primary colors: red, green and blue.
The second method involves using three separate spatial light modulators. Each spatial light modulator modulates light of one of the three primary colors. The light from the spatial light modulators is then projected onto a screen or bought together in some way to make a color image.
The third method involves using a spatial light modulator that sequentially displays red, blue, and green images. In this method, the spatial light modulator is illuminated with red, green and blue light in sequence.
Each of these methods has its disadvantages. In the first method, three pixels are used to represent a pixel of the image. Since the pixels are spread out spatially, the image pixel may appear blurred, as the red, green and blue colors are not in the same location. The blurring effect is particularly noticeable in the form of a color fringe seen at the edge of a colored region.
In the second method, precise alignment of the optics is required to ensure that the light from each of the three spatial light modulators is combined uniformly. While satisfactory alignment may be achieved in the center portions of the image, good alignment is difficult to achieve at the edge of the image. It is found that image pixels located near the edges are spread out into individual colors leading to poor image color quality.
The third method has a problem which is commonly referred to as sequential color artifact. One way to understand this is to imagine a black screen that displays a white vertical bar. An observer who is looking at this display would have an image of the white bar fall on the observer""s retina. However, when the observer""s eye moves quickly to look at something else, the white bar image will appear to smear across the retina. Since the bar is at a different color at a different time, it is not white at any one time. So what the observer""s retina perceives is a red stripe, followed by a green stripe, and followed by a blue stripe. As a result, the white bar appears to look like overlapping colored bars. This is called a sequential color artifact because the colors are observed in sequence.
One other significant drawback of the RGB color display devices is that color information required for a color display device (for example, 3xc3x978 or 24 bits of data for a color computer monitor) is not optimized for bandwidth relative to the sensitivities of the human eye but is equally weighted.
When an observer looks at a spot on a color display, three pieces of information go to the observer""s brain. The first piece of information is how bright the spot is, regardless of its color. The brightness is called luminance. The second piece of information is whether the color is more red or more cyan. This is called red-cyan chrominance. The third piece of information is whether the color is more yellow or more blue. This is called yellow-blue chrominance. The human visual processing system is focused on these three pieces of information, rather than the attributes of red, green and blue as used in the conventional RGB system. Because a human visual system is limited in how much information it can process, it makes approximations based on luminance, red-cyan chrominance, and yellow-blue chrominance. For example more luminance information is retained by the human visual system than chrominance information. To achieve adequate luminance information, more R, G, and B information is required than is necessary for adequate red-cyan or yellow-blue chrominance. As a result, an RGB system is forced to transmit and store excessive chrominance information, or insufficient luminance information, so the quality of color images rendered by the conventional methods is not optimized.
Accordingly, there has long been a need for a color display device that renders images in a way optimized for perception by the human visual system, which improves image color quality and reduces device complexity.
The present invention provides a method of illuminating a pixel on a color display device. A first illuminant source is optically coupled to the modulator pixel which modulates the illuminant source to provide a first color component on a first dual-color axis with a first duration. A second illuminant source is also optically coupled to the modulator pixel which modulates the second illuminant source to provide a second color component on a second dual-color axis with a second duration. The modulated first and the second color components are combined to illuminate the display pixel with the first and second colors of the respective first and second durations whereby the display pixel is perceived to be illuminated by a single color of a single color and intensity. The method renders images in a way optimized for perception by the human visual system. This allows improved image color quality and a reduction in device complexity.
The present invention further provides a method of illuminating a pixel on a color display device. A first illuminant source is optically coupled to the modulator pixel which modulates the illuminant source to provide a first color component having a red/cyan chrominance value and a first luminance value. A second illuminant source is also optically coupled to the modulator pixel which modulates the second illuminant source to provide a second color component having a yellow/blue chrominance value and a second luminance value. The modulated first and the second color components are combined to illuminate the display pixel with the red/cyan and yellow/blue chrominance value colors of the respective first and second luminance values whereby the display pixel is perceived to be illuminated by a single color of a single intensity. The method renders images in a way optimized for perception by the human visual system. This allows improved image color quality and a reduction in device complexity.
The present invention further provides a color display device for displaying a pixel. A first illuminant source is optically coupled to the modulator pixel which modulates the illuminant source to provide a first color component on a first dual-color axis with a first duration. A second illuminant source is optically coupled to the modulator pixel which modulates the second illuminant source to provide a second color component on a second dual-color axis with a second duration. Color component circuitry is connected to the first and second illuminant sources and the pixel for controlling the combination of the first and second color components. The modulated first and the second color components in combination illuminate the display pixel with the first and second colors of the respective first and second durations whereby the display pixel is perceived to be illuminated by a single color of a single intensity. The method renders images in a way optimized for perception by the human visual system. This allows improved image color quality and a reduction in device complexity.
The present invention further provides a color display device for displaying a pixel. A first illuminant source is optically coupled to the modulator pixel which modulates the illuminant source to provide a first color component having a red/cyan chrominance value with a first luminance value. A second illuminant source is optically coupled to the modulator pixel which modulates the second illuminant source to provide a second color component having a yellow/blue chrominance value with a second luminance value. Color component circuitry is connected to the first and second illuminant sources and the pixel for controlling the combination of the first and second color components. The modulated first and the second color components in combination illuminate the display pixel with the red/cyan and yellow/blue colors of the respective first and second luminance values whereby the display pixel is perceived to be illuminated by a single color of a single intensity. The method renders images in a way optimized for perception by the human visual system. This allows improved image color quality and a reduction in device complexity.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.